Plastic composition



Patented June 28, 1.932 I UNITED STATES mam arm:

I ERNEST B. MILLER, OF BALTIMORE, ASSIGIYOR TOTHE SILIQA GEIi COB- PORATION, OF BALTIMORE, MARYLAND, A CORPORATION OF MARYLAND PLASTIC COMPOSITION No Drawing.

The present application which is acontinuation in part of my application SerialNo. 228,692, filed October '26, 1927, relates to plastic compositions, and more particularly to such compositions containing rubber and a finely divided siliceous material, as for example silica gel.

It is customary in the manufacture of rubber articles to incorporate with the rubber a filling material in order to give the article certain properties such as elasticity, 'mechan-' ical strength, resistance to Wear and pres.- sure, and chemical inertncss. A material to be suitable for this purpose must possess the properties of being insoluble in water, chemically inert with respect to the rubber, and capable ofbeing unaffected by heat except at high temperatures, and besides must be in an extremely fine state of subdivision. One of the materials which has been proposed for this purpose is colloidal silicic acid of a' specific gravity of 1.64, the flocculent voluminous precipitate which forms immediately upon the addition of an acid to a silicate solution.

It has been found that incorporating an inorganic gel such as silica gel in a finely divided state in rubber, the rubber article obtained therefrom possesses much greater elasticity and tensile strength or resistance to wear and pressure than rubber articles obtained from rubber compositions wherein colloidal silicic acid of a specific'gravity of 1.64 is employed.

The plastic composition, according to the present invention may be made by incorporating powderedor pulverized silica gelin a rubber mix containing raw rubber and a vulcanizing agent such as sulphur with or without an activator such as zinc oxide and an accelerator as for example, diphenylguanidine. The relative proportions of silica gel andv rubber may be varied according to whether a product richer or poorer in rubber is desired, there being no well defined limits, except that there must of course, be SllfllClGIlt rubber present to bind silica gel. Various methods of intermixmg sub-divided solid materials with rubber are well-known at the present time, and any of these may be used. Such methods do not batch of smolred sheets of rubber consisting the particles of the Application filed November 20. 1930. Serial No. 497,067.

constitute a part of this invention-and are I verized condition the particles do not have any substantially sharp edges. It results, therefore, that the particles of the silica gel will not cut the rubber into which it has been incorporated.

Investigation has disclosed that articles obtained from rubber compositions containing silica gelas the filling material with or without an activator andan accelerator exhibit a greater breaking load or resistance tobreak and also a higher percent elongation or elasticity than do the corresponding products obtained from plastic compositions in which precipitated silicic acid of a specific gravity of 1.64 is used as the filling material. In conducting this investigation a master of 90 parts by weight of rubber and 10 parts by weight of sulphur was first prepared. Stock mixtures consisting of varying proportions of the master batch and precipitated silicic acid of a specific gravity of 1.64 were then prepared, milled, and allowed to stand for 24 hours. The stock mixtures comprised the following proportions.

Stock 1 2 p 3 4 Parts- Parts- Parts Parts Master batch 9O 80' 40 Precipitated silicic acid of 1.64 sp.

gr r 10 20 40 60 N orx. Parts means parts by weight.

the test pieces were then tested in :1 Scott testing machine for the breaking load andbreaking tension or elongation. The results obtained are as follows:

,Stock mixtures consisting of varying pro-. portions of the master batch and powdered silica gel were next prepared, milled, and allowed to stand for 24 hours. The stock mixtures comprised the following proportions.

Stock 10 11 12 1:;

Parts Parts Parts Parts Master batch"; 9c 80 60 40 Silica gel 10 6O Nora-Parts means parts by weight.

Portions of each of the stock mixtures 10, 11, 12 and 13 were then vulcanized in a platen press at a temperature of 143 C. for 60 minutes. The other portions of said mixtures were vulcanized at the same temperatures for 75 minutes. The slabs, after vulcanization, were allowed to stand for 24 hours whereupon test pieces were cut from each slab representing eachcure. The test pieces were then tested in a Scott testing machine for the break ing load and breaking tension or elongation. The results obtained are so follows:

Minutes for Breaking Stock vglcania- 23 tiension or 1%: a lbs/sq. in. 5 2

10 60 559 lbs 800 75 1429 795 Stock mixtures consisting of. varying proportions of precipitated silicic acid of a specific gravity of 1.64, the master batch, an organic accelerator and. an activator therefor were next prepared, milled and allowed to stand for 24 hours. The stock mixtures comprised the following proportions.

Stock 5 6 7 8 Pa rta Parts Parts Parts Master batch 90 80 60 40 Precipitated siiieic acid of 1.64 sp. gr 10 20 4O 60 Zinc oxide I 4. 5 4 3 2 Diphenyiguanidine 0. 9 0. 8 0. 6 0. 4

N0'1'E.'Pa:ts means parts by weight.

Stock mixtures 5, 6, 7 and 8 were then treatcd in exactly the same manner as stock mixtures 1, 2. 3 and 4 and after vulcanization were tested for the breaking load and breaking tension or elongation. Theresults are as follows:

q rii t ii i- Breaking llgiiil o r took ization at g in elongation 5 60 2041 lbs 625 t 75 985 475 6 a 60 786 380 75 978 430 Stock mixtures consisting of varying portions of powdered silica gel, the master batch, an organic accelerator and an activator therefor were next prepared in the same manner as described in connection with the other experiments. The stock mixture comprised the following Stock NOTE.Pml;S means parts by weight.

Stock mixtures 14, 15, 16 and 17 were then treated in the same manner as stocks 10, 11, 12 and 13 and after vulcanization were tested for the breakingload and breaking tension or elongation. The results obtained were as follows:

Minutes for vulcanization at 143 0.

Breaking tension or elongation Breaking Stock 10 lbs/sq. in.

Thus, articles obtained from rubber plastic compositions made according to the present invention exhibit enhanced properties asregards tensile strength and elasticity. I T Although the invention has been described in connection with silica gel it is to be understood that other inorganicgels, as for ex ample gels containing an oxide of tin, tungsten, titanium, or aluminum, or mixtures of said oxides may be used.

The term inorganic gel as used in the claims designates the solid, hard material having ultra-microscopic pores obtained from a dried or nearly dried jelly.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. A rubber composition consisting of rubber having incorporated therein a powdered, hard, porous, highly adsorptive inorganic gel selected from the group consisting of-the oxides of silicon, tin, tungsten, titanium, aluminum, characterized in that it has a. tensile strength and elasticity much greater than that of a similar composition containing an equal weight of the oxide in a difl'erent form. 1 2. A rubber composition consisting of rubher having incorporated therein powdered I5 hard-,-porous, highly adsorptive silica gel,

characterized in that it has a tensile strength and elasticity much greater than that of a similar composition containing an equal Weight of the silica in a different form.

In testimony whereof I hereunto aflix my signature. I ERNEST, B. MULLER. 

